"Mapping Venus: The Venus Express Mission"

Interview of Eric Villard, MSS-2002

(December 2005)

The planet Venus has captured the imagination of humans for centuries. Over the past decades, a few space missions have started to uncover the secrets of Earth's closest neighbour, but there is still much to learn! Eric (MSS'02) is currently working on the exciting European Venus Express mission that will orbit Venus by April 2006 and he kindly agreed to share with us some information.

Could you tell us a little bit about yourself and how you got involved in the Venus Express mission?

Sure! My name is Eric Villard, I am 27 and I currently work at the Aeronomy Service of CNRS (Centre National de la Recherche Scientifique) in Verrieres-le-Buisson, France, on an instrument that is called SPICAV (for Spectroscopic Investigation of the Characteristics of the Atmosphere of Venus) and which is embarked on the European Space Agency (ESA) Venus Express mission which has just lifted off from Baikonour last November 9.

Aeronomy is quite a recent science. It had always been a part of meteorology until 1954, when the name was first introduced, and until 1957-58, the International Geophysical Year, when it was recognized as a science. The objective of aeronomy is to study the physical processes that occur in the middle and upper atmospheres. At the beginning, it was only the Earth's atmosphere but as it became possible to put spacecrafts in orbit around extraterrestrial bodies, aeronomy started to study also planetary atmospheres.

How I joined the Aeronomy Service is not straightforward. I always had a fascination for space and astronomy. When I was a child, I would spend entire nights outside during the Perseids storms, just to count the shooting stars and I would graph these values as a function of the date, just to see how they would evolve. I also got the virus of hamradio from my father. Hamradio or amateur-radio, is a hobby that can take you very far in distance but also in height.

Some amateurs are spending a lot of time (and also a lot of money) in EME (for Earth-Moon-Earth) communications, which consist in using the Moon as a reflector for the radio waves. This is of course not a very efficient way of communicating but the challenge is to get a signal at the end when you know that the attenuations can be more than 200dB! Personally, I did not get that far. I got "only" to the Mir Space Station! In fact, there was a hamradio transceiver onboard Mir (there is also one on the ISS) and amateurs all around the world could talk to the cosmonauts. Of course, only during their free time. So, one day, after obtaining my hamradio certificate with success, I tried... and I succeeded!

Valery Polyakov was onboard the station at that time. I will always remember my very first contact (sounds like Star Trek): I shouted "Dad!! I got a contact with Mir!!" I was only 16. You can imagine the impact. Then, I spent a lot of time learning about satellite tracking softwares, 2-line elements and orbits, in order to predict the passes above my house. And it turned out that most of the best passes (with a high elevation above the horizon) were in the middle of the nights. So, I would wake up in the middle of the night, just to listen to or try to contact the cosmonauts. My father was really supportive. Actually, he would also wake up in the middle of the night, to help me. Then, two years later, I left my home in Africa and moved to France, and I stopped waking up in the middle of the nights because I did not have any receiver anymore.

I then followed the classical path to the Engineer's degree, which I obtained in electronics, signal processing and physics. I was about to start a career in electronics, when I applied to ISU and I got accepted. This was the turn. A couple of months after graduating, I learned that a position was available within the SPICAV team, I got interviewed, passed and started the same day! Then, a couple of months later, I obtained a scholarship from CNES (Centre National d'Etudes Spatiales) to prepare a PhD thesis in parallel. Today, when I look back, I feel very lucky that I have applied to ISU.

Do we know already very much about Venus?

We know a lot, that is for sure! The Russians have sent a lot of space missions in orbit and on the ground of our sister planet. We know its composition (mainly CO2, a few percents of N2 and traces of water vapour), we know most of the physical processes that occur today, we also know that the temperature and the pressure on the surface are quite high: about 450°C and 95atm. This is probably hell as we imagine it. We know that there are sulfuric acid rains that prevent any life forms, as we know them, to appear. We also know that the atmosphere is rotating around the planet in about 4 Earth's days! It is called "super rotation". The mechanism, however, we do not know exactly. We also know that the planet has no magnetic field, which, on Earth, protects us from the Solar radiation. This may be because the planet rotates very slowly: 243 Earth's days to do a complete rotation. But this is not sure.

There is however one thing we do not know: where has all the water gone? Because Venus is quite comparable in size and density with Earth. We can therefore assume that its formation was quite comparable with our planet, with a lot of hydrogen molecules combining with oxygen molecules to form water vapor. However, today, Venus is crushed by an extreme greenhouse effect and there is very little water in the atmosphere. Why and where did all the water go? How has this greenhouse effect started? These are questions whose answers may help us preventing our planet to follow the same path.

What are the objectives of Venus Express?

The mission consists only of an orbiter, contrary to its sister mission, Mars Express. Therefore, the objective will mainly be to study the atmosphere of Venus: detailed study of the composition, better understanding of the physical processes, study of the plasma environment, analysis of the interaction between the upper atmosphere and the Solar wind, study of the surface and lower atmosphere physics and chemistry thanks to the narrow infrared windows which have been discovered recently...

The spacecraft embarks a suite of 7 top scientific instruments (ASPERA, MAG, PFS, SPICAV, VERA, VIRTIS, VMC) which should be able to unfold most of the mysteries of the morning star and probably, ask new questions.

Could you describe the instrument you have been working on?

SPICAV (for Spectroscopic Investigation of the Characteristics of the Atmosphere of Venus) is a large-band and high-resolution spectrometer. It actually includes three spectrometers: one in the ultraviolet domain (110 to 320nm), another one in the visible and near-infrared domains (0.7 to 1.7microns) and one in the middle-infrared domain (2.3 to 4.4microns).

Each spectrometer uses a different technique. The UV channel is based on a holographic grating and intensified CCD (Charge Couple Device). This combination provides a very large dynamic of sensitivity, allowing observing strong sources (the Sun) as well as very weak sources (high magnitude stars).

The second channel uses a novel device called AOTF (for Acousto-Optic Tunable Filter). It is a transparent crystal which has the very interesting property that it only lets a very narrow part of the light spectrum go out in one direction when it is vibrated at a specific frequency. How we use this property is very simple: we collect the light at the entrance of the instrument and focus it at the entrance of the crystal, then we apply a radio-frequency on the crystal, which lets some light go out of the crystal and we measure this light with a photodetector. Then, we slightly shift the frequency of the vibration, which in turn, slightly shifts the wavelength of the light exiting the crystal and so on. Eventually, we obtain a complete spectrum with as many points as there were steps of frequency. The big difference with the UV channel is that one complete spectrum is not obtained instantaneously, which can be a problem sometimes.

As for the third channel, it is using both techniques, the grating and the AOTF, to reach a super resolution that would be very difficult to obtain otherwise given the stringent volume and mass constraints. To summarize: the grating is the dispersive element (it means that it acts like the surface of a CD: it separates the wavelengths of the light). However, the way we use this grating implies that many orders will overlap on the detector (orders are somehow like the harmonics of radio: they are located at multiples of the initial value). Higher orders are usually not a serious concern because they are quite attenuated. In our case, they are not. That is where the AOTF comes in, to separate the various orders. This may be a little difficult to understand but the result is quite amazing: an average resolution of 0.08cm-1 between 2.3 and 4.4microns, for a mass of about 6kg!

When Venus Express finally arrives in the Venusian orbit in April 2006, how long is the mission is expected to last?

The spacecraft will be inserted in orbit around Venus on April 11, 2006. Then, it will slowly reach its final orbit: elliptical, period of 24h, apocenter at 66,000km and pericenter at 250km.

In the meantime, a few tests will be run to confirm the good health of the spacecraft. And once the commissioning has been completed, it will be handed over to the science operations and the mission will start. The initial duration is 500 Earth's days with a possible extension of another 500 Earth's days. A total of two years and a half which should give a wealth of information on a fascinating planet.

Want to know more about Venus and the Venus Express mission?

After Eric's exciting account, you may want to learn more about Venus, the closest planet to Earth, and the Venus Express mission. You can check the latest news concerning the mission, with also great pictures and movies, on this European Space Agency dedicated website.

Also, if you want to get in touch with Eric to learn more of his experiences with the mission, you may reach him at .

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